There has been proposed a boiler system including a boiler group provided with a plurality of boilers configured to combust at a changed combustion rate, and a boiler number control device configured to control a combustion state of the boiler group in accordance with a required load. Such a boiler system includes a steam header configured to store steam generated by the plurality of boilers, and the steam header supplies a loading machine with the steam.
Widely used to date as such a boiler system is a step value control boiler configured to combust at a stepwisely changed combustion rate. Also starting to spread in recent years is a boiler system including a proportional control boiler configured to combust at a continuously changed combustion rate.
A step value control boiler indicates an N-point boiler configured to combust at a plurality of stepped combustion points (e.g. a three-point boiler having a combustion stopped point, a low combustion point, and a high combustion point). Such a step value control boiler has a combustion rate changed stepwisely (e.g. every 50%). In contrast, a proportional control boiler has a combustion rate changeable by every percent or the like. The proportional control boiler can be regulated more delicately than the step value control boiler and thus has improved pressure stability.
In a boiler system including step value control boilers, a boiler number control device preliminarily sets combustion patterns of the respective boilers and causes each of the boilers to combust in a combustion pattern corresponding to steam pressure of a steam header to control a combustion state of the boiler group (see Patent Literature 1).
In a boiler system including proportional control boilers, a boiler number control device preliminarily sets target pressure and calculates a control amount according to a deviation between steam pressure of a steam header and the target pressure to control a combustion state of a boiler group (see Patent Literature 2).